Semi trucks consist of a tractor and a trailer. For legal and safety concerns the loads carried in the trailers must meet state and federal weight requirements. This can be accomplished most often by positioning the trailer over the tandems in the rear of the trailer. Weight limitations apply to the steers, the drives and the tandems. Movement of the trailer over the tandems affects the weight at all three locations, the steers, the drives and the tandems. The trailer is constructed to slide back and forth over the tandems until the proper position is achieved and then locked into that position. Two parallel rails, fastened longitudinally underneath the trailer (sometimes referred to as the main frame) are fitted over corresponding rails on the tandems (sometimes referred to as the sub-frame). Holes in the trailer rails are positioned to engage extendable pins located on the tandems through holes in the tandem axle rails. Two or four pins are generally employed to lock the trailer and tandems together. The pins are retracted to permit the trailer to slide back and forth over the tandems. The pins are extended to lock the trailer to the tandems when the proper position is achieved to meet positional weight requirements. The mechanism used to extend and retract the pins is located on the tandems and moves all of the pins simultaneously. Holes in the trailer rails are located so they can match the locations of the pins. Thus lining up a hole on one trailer rail with a locking pin on one side of the tandems will simultaneously line up with a hole on the trailer rail on the other side of the trailer with a locking pin on the other side of the tandems.
The difficulty of locating the trailer in the proper position over the tandems axle is that the driver sitting in the tractor cannot see the relative position of the trailer over the tandems at the back of the trailer. After selecting the locking pin hole in the trailer rails to achieve proper weight and balance, a driver working alone must climb back into the cab of the tractor and slide the trailer until he/she thinks the correct position has been acquired. This action is repeated after every move the driver makes to position the trailer over the tandems and determine the relative position of the selected hole in the trailer rail to the pins in the tandems. The driver may have to make several trips climbing in and out of the tractor before positioning the trailer over the tandems at the selected location.
The prior art contains many examples of means for locating the trailer of a semi truck over the tandem axle. With varying degrees of complexity the prior art accomplishes this by some sort of sensor or trigger that detects when the trailer is in proper position and turns on a switch that activates a signal that can be detected by the driver without getting out of the tractor. Some of the newer semi trucks come with built in sensors and signals so assist the driver with this task. Most of the older trucks do not.
U.S. Pat. No. 5,617,072 discloses a mechanism to assist the driver to position the front of the trailer over the fifth wheel assembly mounted on the tractor or the back of the trailer over the tandem axle assembly. In each case the switch is located oh the fifth wheel assembly or the tandem axle assembly while the trigger part of the signaling apparatus is attached to a suitable position on the frame or other structure of the vehicle. A light signals the driver when the proper position is achieved.
U.S. Pat. No. 5,460,237 discloses an air-powered actuator for retracting the locking pins and light means to signal the driver to determine that the pins are in position for retraction. It does not disclose a signal capable of determining when the locking pins are in position to engage selected holes in the trailer rail.
U.S. Pat. No. 5,678,834 discloses means for providing a remote indication of the positioning desired by the driver of a semi truck while the driver remains in the cab. However it does so employing a much more complicated set of components. Thus it employs a rod fitted in a tube and means for attaching one end of the combination to the tandem axle as well as means for securing the adjustment end of the rod within the tube. It also employs a spring attached at one end to the locking pin release handle. Finally it employs a separate visible indicator attached to the trailer.
U.S. Pat. No. 6,354,642 discloses a tool for positioning a tandem rig under a trailer of a semi truck. The tool attaches to the tandem and applies force to the handle, which unlocks the positioning pins. It then signals the driver in the cab that the positioning pins have been freed from their locked position. The tool is not designed to signal the driver when the positioning pins are in position to be locked.
The present invention differs substantially from the above in several ways. First the switch assembly is a single piece that attaches to a single location on the trailer rail. When the switch reaches the selected locking pin location to achieve proper weight and balance in the trailer, it turns on the signal that alerts the driver that the trailer is in the selected position for extending the locking pins. Additionally the Locking Pin Locator comes in a small compact carrying case for easy storing. Being more portable and compact than its prior art alternatives, it performs this function in an inexpensive and simple manner.